a semaphore is a synchronization primitive used for coordinating access to a shared resource between
multiple concurrent processes or threads.
A semaphore is essentially a variable that is used to manageaccess to a shared resource by controlling the number of threads that can access the resource at any given time. A semaphore contains an integer value that is initially set to a specific value. The semaphore can be incremented and decremented, and the value of the semaphore is checked before allowing a thread to access the shared resource.
A semaphore can be either binary or counting. A binary semaphore can have a value of either 0 or 1, and it is used to indicate whether a shared resource is currently in use or available. A counting semaphore can have a value greater than 1 and is used to limit the number of threads that can access a shared resource simultaneously.
When a process or thread wants to access the shared resource, it requests alock on the semaphore. If the semaphore value is greater than zero, the process or thread is granted access to the resource, and the semaphore value is decremented. If the semaphore value is zero, the process or thread is blocked and added to a queue until the semaphore value becomes nonzero.
When a process or thread releases the shared resource, it signals the semaphore by incrementing its value. If there are any waiting processes or threads in the queue, one of them is granted access to the resource. Semaphores are often used in multithreaded or multiprocessing systems to prevent race conditions and ensure that concurrent processes do not interfere with each other when accessing shared resources. Semaphore-based synchronization is an efficient way to manage shared resources and prevent deadlocks by ensuring that multiple processes do not simultaneously access the same resource